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22 Cards in this Set
- Front
- Back
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what does the P wave represent
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atrial depolarization
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what does the QRS complex represent
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ventricular depolarization
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What doe sthe T wave represent
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ventricular repolarization
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What is the normal calibration of an ECG sheet
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25mm or 5 big squares = 1 second, use this to calculate HR and intervals
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What is a normal P-R interval
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.16 seconds
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What is a normal QT interval
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.35 seconds
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Describe the orientation of the axis of leads I, II, and III including where their + and - ends are
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Lead I-right arm - to left arm + end; Lead II-right shoulder negative to left leg positive; Lead III-Left shoulder negative to right leg positive (remember the positive leads are down and left, follow depolarization pattern)
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what is einthoven's law
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I + III=II be cafeful with signs!!
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how do you calculate the potential in a lead
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Plus-Minus, watch signs!
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How do you determine a projected lead vector
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from the given net axis, draw a line perpendicular from the tip of the net vector to the axis of the lead that you are trying to determine
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Descrie how the orientation of the mean electrical axis of the heart changes as the ventricles depolarize
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Beging pointing slightly towards left down septum, as depolarization continues arrow gest longer, near the end the only area left not depolarized is the top of the left ventricle so the arrow points there. At complete deoplarization there is no vector because there is no potential differnece at that instant
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Why is the T wave positive even though it represents repolarization
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the outer apical surface of the ventricle repolarizes first and then it moves backwards up the septum. This means that the vector will still point towards the apex (It's a double backwards situation, hyperpolarization is the reverse of depolarization and but the direction of hyperpolarization is the reverse of depolariation so you wind up with the same direction)
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An SA block would show on on an ECG as
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p wave cessasstion and a slower HR
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An AV block would show up on an ECG as
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PRlonged P-R (more than 0.16 sec) interval, dropped beat, and dissociation of atrial rate and ventricular rate
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How would an intraventricular block show up on an ECG
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altered size and shape of QRS
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How would atrial fibrillation show up on an ECG
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variable times between QRS complexes, fast heart rate
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what is the normal mean electrical axis or the ventricular QRS
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positive 59 degrees
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How does angulation of the heart change the MEA
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MEA shifts towards direction of angulation so if the heart is shited left (end of deep exhalation, lying down, obesity) the the axis shifts left. if the angle is the the right (end of inspiration, standing up, tall skinny people) the axis shifts right
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In which direction will the MEA shift if a ventricle is hypertrophied? why?
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the axis shifts towards the hypertrophied ventricle because 1. there is more muscle there so there is greater electrical potential generated 2. more time is required to depolarize the hypertrophied ventricle so the normal ventricle depolarizes first causing a strong vector from the normal side of the heart toward the hypertrophied side
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How would the MEA shift in left bundle block
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When the left bundle is blocked, the right ventricle depolarizes much faster than the left so a vector would project from the right towards the left resulting in a left axis deviation, note that in addition to axis deviation, the QRS complex will also be prolonged
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What would show up on an ECG if the purkinje fibers were blocked
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prlolonged QRS (more than 0.09 seconds)
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describe the concept of current of injury
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injured areas of the heart remain depolarized (negative on the outside) all of the time, current will then flow between the normal polarized areas and the pathologically depolarized area, this will mess up the ECG
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